Customers announcing communities to SP of SP

[Jason Lixfeld <jason+nanog () lixfeld ca>]

Hi,

Consider the following scenario:

- Customer A is a customer of SP A
- SP A is a customer of SP B
- SP B has a traffic engineering community implementation 

With regards to using BGP communities for TE:

- Does SP A write their own community implementation that maps to (some portion of) the community implementation of SP 
B?
- Does SP A write their own community implementation that has no mappings at all to the community implementation of SP 
B; any TE that is required to be pushed to SP B is done by some dialog and coordination between Customer A and SP A?
- Does SP A allow Customer A to announce prefixes tagged with SP B’s communities[1][2]
- Is this sort of thing really complicated today, but one of the goals of draft-heitz-idr-large-community?

[1] Customer A has knowledge of SP A’s upstream SP B
[2] This opens up a can of worms where SP A or SP B implements some communities prefixed with reserved ASes, so we’ll 
assume that SP A implements some method of allowing communities prefixed with ASes of SP A and SP B only.

Thanks!